The axial cooling system of a motor in the prior art is mostly constructed by providing axial ventilation holes in the yoke of the stator. The rise of the temperature of the motor is lowered by cooling the yoke. When the motor operates, the heat is generated mostly by copper wires, secondly by the eddy-current in silicon steel sheets. The teeth of the motor are the second highest temperature area after the stator windings. Therefore, the heat cannot be dissipated swiftly through the cooling manner of disposing ventilation holes in the yoke of the stator.
In order to solve the problems above, some permanent magnet motors adopt the cooling manner of disposing circular ventilation holes in the teeth of the stator of the motor, and the heat of the teeth is dissipated through the coolant flowing through the circular ventilation holes. This cooling manner enables the heat-exchange fluid to carry out heat exchange at the teeth of the motor, where heat is generated most intensively, but there is an air gap between the inner circle surface of the stator and the outer circle surface of the rotor, thus part of the heat-exchange fluid will flow away through the air gap, affecting the heat dissipation from the teeth of the stator core and causing air friction loss.